Herpes simplex virus (HSV) type 2 is a common sexually transmitted viral agent which is the leading cause of genital ulcers. In the United States, the prevalence of this disease exceeds 45 million, affecting more women than men. Genital HSV-2 infection often results in the establishment of latency in the sacral root ganglia, with frequent reactivation and productive infection in the mucosal epithelium. Although HSV-2 is treated symptomatically with anti-viral agents such as acyclovir, currently no cure exists for this debilitating disease. The goal of the studies proposed is to define and understand the cellular and molecular mechanism of how protective immunity is generated to HSV-2 infection at the genital mucosal surfaces. Prior studies demonstrated that protective immunity is mediated by CD4+ T lymphocytes secreting IFNg. Data from our own studies revealed the critical importance of dendritic cells in generating Th1 responses following intravaginal HSV-2 infection. Further, we demonstrate that the activation of dendritic cells (DCs) and induction of Th1 responses during HSV-2 infection require toll-like receptor (TLR) signaling. With the use of a mouse model for genital herpes infection, this proposal will systematically define the intercellular and intracellular signals that govern the recruitment and activation of dendritic cells leading to priming of CD4+ T lymphocytes to secrete IFNg. The first aim will assess the mechanism by which the dendritic cells are recruited to the sites of primary infection, and to evaluate the functional roles of distinct subsets of DCs in the generation of anti-HSV-2 immunity. The second aim will systematically identify the TLRs that recognize HSV-2 and to determine the viral ligands that bind to the respective TLRs. A final aim will examine the in vivo role of TLR-mediated recognition of HSV-2 by different host cell types. The proposed experiments will provide novel and critical information on the mechanism of generation of protective immunity within the female genital tract to HSV-2. Since productive Th1-based immunity is important in defense to most intracellular pathogens, the insights provided by the proposed studies should eventually aid in the designing of rational approaches to prevention of the spread of HSV-2 and other sexually transmitted diseases.